Physiological responses to cold stress in maize during early phases of development
Earlier spring planting to maximize the duration of the growing season has increased the importance of early-season cold tolerance in maize ('Zea mays' L.). The objectives of this study were to assess the response of several physiological parameters associated with cold tolerance in maize during early development and to quantify variability in the response to cold stress among 49 maize inbred lines and three hybrids. At the 7-leaf tip stage, maize inbred lines and hybrids were subjected to two day/night temperature regime treatments, 25/15°C (control) and 15/3°C (cold). Carbon exchange rate, leaf chlorophyll content, quantum efficiency of Photosystem II, stomatal conductance, dry weight, root/shoot ratio, and rate of development were measured at the 8-leaf tip stage for genotypes under both treatments. The cold treatment effects were significant for all parameters except root/shoot ratio. Genotypes differed in their response to cold stress for all parameters except for dry weight among inbred lines. Hybrids differed only in their cold stress response of carbon exchange rate, chlorophyll content and stomatal conductance. The results show that there was genetic diversity for most traits investigated and that total dry weight under optimal conditions and response to cold stress of leaf carbon exchange rate and rate of development may be good discriminators of cold tolerance during early phases of development.